Psychophysical DUI Test

What is the Psychophysical Test in a DUI?

A psychophysical test is a means of determining the level of physical and mental impairment of a driver in a suspected DUI. Abilities crucial to safe driving such as, coordination, balance and the processing of information, are tested in a psychophysical test. When suspected of a DUI, the officer begins the psychophysical test as soon as he/she comes in contact with the driver, paying special attention to the drivers processing skills.


A preliminary breath test (PBT) can be administered in a suspected DUI to confirm the level in impairment of a driver. However, a PBT result cannot be used as evidence against the suspect in a Utah court.


Another test or observation that can be administered is a Horizontal Gaze Nystagmus (HGN) which refers to an involuntary jerking as a driver gazes forward. The jerking is involuntary and the person experiencing it is unaware that it is happening. Such symptoms become extremely noticeable when a person is heavily impaired. As a person’s blood alcohol concentration increases, the eyes will begin to jerk sooner than usual as they attempt to move them from side to side. This test is what police officers heavily use to confirm their suspicion of a DUI. When administering the HGN test, an officer will have the driver follow the motion of a small object, such as a penlight or the end of a writing utensil, with his/her eyes only. The officer will always start with the suspects left eye in an HGN test. With each eye there are three clues that the officer will look for in a HGN test.

1) Does the eye move smoothly or does it makes involuntary attempts to move?

2) When the eye moves to a far side and kept there for several seconds does it involuntary jerk?

3) Does the eye start to jerk before a 45-degree angle when moved to the side? With each eye there are three clues that can be evident, so if four-or-more clues are present in both eyes together officers believe that the test is over 70% accurate. That is why the HGN test is often used to confirm their suspicions.

Salt Lake DUI Defense Lawyer

The psychophysical tests administered by law enforcement can be the subject matter of dispute and the means to a good defense in a Utah DUI case.  Our Utah criminal defense lawyers know how to put together a solid defense revolving around how the tests were carried out.  Call us at 801.618.1334 or email us to set up an appointment with a DUI Defense attorney.

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